As shown in FIG. 1, when a lobectomy is performed a space 10 is created in a chest cavity 18 by the removal of the unhealthy lobe. Removal of the lobe typically results in the diaphragm 14 rising as the remaining healthy lung 16 attempts to fill the newly created space 10. The remaining healthy lung 16 will hyper-expand to an extent to either partially or fully fill the excess space 10. Such a hyper-expansion interferes with normal respiration of the patient as will be discussed in more detail below. A similar lung hyper-expansion can also occur with patients suffering from emphysema, a lung disease. As a result of this lung hyper-expansion, patients can experience exertional dyspnea which can be extremely uncomfortable, limits one's activity, and potentially can become life-threatening.
Referring to FIG. 2, a standard spirometry chart is shown which depicts lung volumes. It is believed that with a lobectomy (or with emphysema) there is not only a decrease in Vital Capacity (VC) and Inspiratory Reserve Volume (IRV) but patients also experience an increase in the Residual Volume (RV) of the remaining native lung (which is essentially and functionally a physiologic dead space), as well as a decrease in Expiratory Reserve Volume (ERV). The increase in RV of the remaining lung corresponds to the hyper-expansion of the remaining healthy lung. The hyper-expansion of the remaining lung also partially accounts for the decrease in ERV and IRV. A similar phenomenon of lung hyperexpansion occurs with emphysema except that in this case the whole lung is diseased and no lung has been removed.
To prevent the remaining lung (or lobe(s)) from hyper-expanding under these situations, it has been described that one may implant a prosthetic into the chest cavity to help restore the normal size, shape, and mechanics of the remaining native lung tissue and allow for more normal respiration to be achieved.
In particular, known implantable lung prosthetics placed in the chest function essentially as static space occupiers that do not change in their size and shape. The problem with known lung prosthetics is that the remaining native lung tissue with which the prosthetic works is not static in size and shape. During normal respiration, native lung tissue will change in size and shape from about 12 to about 20 times a minute. At the same time, the chest cavity within which the native lung and lung prosthetic reside also changes in size and shape about 12 to about 20 times per minute during respiration.
With known static-sized lung prosthetics, it is postulated that with inspiration (when the chest cavity increases in size and volume) the lung prosthetic will become surrounded by empty space or the remaining native lung hyperexpands to fill that extra space. Then, with deep expiration (when the chest cavity decreases in size and volume) the same lung prosthetic can become too big for the reduced sized space that it occupies. As a result, during normal respiration known implanted lung prosthetics do not mimic the change in lung size and volume of the excised lung or the change in size and volume of the chest cavity.
Another known implanted prosthetic includes a pressure relieving area which provides a place for excess fluid to decompress as a safety measure during changes in thoracic pressure, such as during an airplane flight. However, this known prosthetic design does not allow fluid to pass into and out of the prosthetic as the patient breathes during normal respiration. As a result, known implanted lung prosthetics having pressure relieving areas also do not mimic the change in lung shape and size that occurs during normal respiration.
As such, known implanted prosthetics do not effectively prevent the exacerbation of perturbations in physiologic lung volumes (such as Residual Volume (RV), Expiratory Reserve Volume (ERV), and Inspiratory Reserve Volume (IRV)) and therefore are incapable of properly ameliorating exertional dyspnea that patients can experience.
Accordingly, there exists a need for a prosthesis that can change in size and shape as the patient breathes in and out so as to mimic the operation of a real lung during normal respiration while at the same time filling out the chest cavity as the chest changes in size and volume during respiration.